Transient voltage suppressor circuit, and diode device therefor and manufacturing method thereof

ABSTRACT

The present invention discloses a transient voltage suppressor (TVS) circuit, and a diode device therefor and a manufacturing method thereof. The TVS circuit is for coupling to a protected circuit to limit amplitude of a transient voltage which is inputted to the protected circuit. The TVS circuit includes a suppressor device and at least a diode device. The diode device is formed in a substrate, which includes: a well formed in the substrate; a separation region formed beneath the upper surface; a anode region and a cathode region, which are formed at two sides of the separation region beneath the upper surface respectively, wherein the anode region and the cathode region are separated by the separation region; and a buried layer, which is formed in the substrate below the well with a higher impurity density and a same conductive type as the well.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a transient voltage suppressor (TVS)circuit, and a diode device therefor and a manufacturing method thereof;particularly, it relates to such TVS circuit wherein a higher forwardcurrent can be sustained, and a diode device therefor and amanufacturing method thereof.

2. Description of Related Art

FIG. 1A shows a typical TVS circuit 1. The TVS circuit 1 is coupled to aprotected circuit 2, for limiting amplitude of a transient voltage froman input/output (I/O) pad 3, so as to protect the protected circuit 2from damages caused by the transient voltage (by static charges, forexample). In general, the TVS circuit 1 includes a suppressor device S1for clamping the amplitude of the transient voltage and for absorbing anexcess current path. Because the suppressor device S1 needs to release ahigh current in a very short time, a large area PN junction is required,resulting in a very high parasitic capacitance. Therefore, during normaloperation, the operation speed of the protected circuit 2 is lowered bythe parasitic capacitance, and thus the application range of theprotected circuit 2 is limited.

FIGS. 3A and 3B are a schematic cross-section diagram and a simulationcurve showing a diode device 100 of the prior art TVS circuit 1 and itsimpurity concentration distribution, respectively. As shown in FIG. 3A,the prior art diode device 100 is formed in a substrate 11, and includesan N-type well 13, a field oxide region 12, isolation regions 12 a, aP-type anode region 15 and an N-type cathode region 16. FIG. 3B is thesimulation curve showing the impurity concentration from an uppersurface of the P-type anode region 15 downward in the prior art diodedevice 100.

A method for increasing the operation speed of the protected circuit 2is, as shown in FIG. 1A, providing at least one diode device D1 with alower parasitic capacitance between the protected circuit 2 and thesuppressor device S1. The PN junction of the diode device D1 and the PNjunction of the suppressor device S1 are connected in reverse series,such that a current may flow through the diode device D1 in a forwarddirection, and the suppressor device S1 can absorb and release a highcurrent once it occurs; i.e., by connecting a capacitor with lowcapacitance and a capacitor with high capacitance in series, the totalcapacitance is reduced to increase the operation speed of the protectedcircuit 2. However, though this method can suppress the problem of thehigh capacitance of the suppressor device S1, the diode devices D1 stillneed to sustain the high current induced by the transient voltage fromthe I/O pad 3. And if the TVS circuit 1 has a lower capacitance, thecurrent which the TVS circuit can sustain is reduced, and thus theapplication range of the TVS circuit 1 is limited.

In view of above, to overcome the drawbacks in the prior art, thepresent invention proposes a TVS circuit, and a diode device thereforand manufacturing method thereof so that the TVS circuit may sustain ahigher forward current, and the protected circuit may have a broaderapplication range.

TOTAL OF THE INVENTION

A first objective of the present invention is to provide a transientvoltage suppressor (TVS) circuit.

A second objective of the present invention is to provide a diode devicefor a TVS circuit.

A third objective of the present invention is to provide a manufacturingmethod of a TVS circuit.

To achieve the objectives mentioned above, from one perspective, thepresent invention provides a transient voltage suppressor (TVS) circuitfor coupling to a protected circuit to limit amplitude of a transientvoltage which is inputted to the protected circuit, the TVS circuitcomprising: a suppressor device, which has a PN junction for limitingamplitude of the transient voltage; and at least one diode device, whichis coupled between the protected circuit and the suppressor device,wherein the diode device has a PN junction which is coupled to the PNjunction of the suppressor device in a reverse direction; wherein thediode device is formed in a first conductive type substrate, which hasan upper surface, the diode device including: a well having the firstconductive type or a second conductive type, which is formed in thesubstrate beneath the upper surface; a separation region, which isformed in the substrate beneath the upper surface, wherein theseparation region is located in the well from top view; a firstconductive type anode region, which is formed beneath the upper surfaceat one side of the separation region; a second conductive type cathoderegion, which is formed beneath the upper surface at the other side ofthe separation region, wherein the cathode region is separated from theanode region by the separation region; and a buried layer, which isformed in the substrate below the well, wherein the buried layer has asame conductive type with the well, and its impurity concentration ishigher than that of the well.

From another perspective, the present invention provides a diode devicefor a transient voltage suppressor (TVS) circuit, the TVS circuitincluding a suppressor device having a PN junction, wherein the diodedevice has a PN j unction which is coupled to the PN junction of thesuppressor device in a reverse direction, and the diode device is formedin a first conductive type substrate which has an upper surface, thediode device comprising: a well having the first conductive type or asecond conductive type, which is formed in the substrate beneath theupper surface; a separation region, which is formed in the substratebeneath the upper surface, wherein the separation region is located inthe well from top view; a first conductive type anode region, which isformed beneath the upper surface at one side of the separation region; asecond conductive type cathode region, which is formed beneath the uppersurface at the other side of the separation region, wherein the cathoderegion is separated from the anode region by the separation region; anda buried layer, which is formed in the substrate below the well, whereinthe buried layer has a same conductive type with the well, and itsimpurity concentration is higher than that of the well.

From another perspective, the present invention provides a manufacturingmethod of a diode device for a transient voltage suppressor (TVS)circuit, wherein the TVS circuit includes a suppressor device having aPN junction, and the diode device has a PN junction which is coupled tothe PN junction of the suppressor device in a reverse direction, themanufacturing method comprising: providing a first conductive typesubstrate, which has an upper surface; forming a well having the firstconductive type or a second conductive type in the substrate beneath theupper surface, and forming a buried layer in the substrate below thewell, wherein the buried layer has a same conductive type with the well,and its impurity concentration is higher than that of the well; forminga separation region in the substrate beneath the upper surface, whereinthe separation region is located in the well from top view; forming afirst conductive type anode region beneath the upper surface at one sideof the separation region; and forming a second conductive type cathoderegion beneath the upper surface at the other side of the separationregion, wherein the cathode region is separated from the anode region bythe separation region.

The suppressor device may include: a varistor device, a Zener diode, twoZener diodes connected in reverse series, or a gate-less metal oxidesemiconductor (MOS) device.

In one embodiment, the separation region includes a field oxide regionor an intrinsic semiconductor region.

In another embodiment, the TVS circuit includes a plurality of the diodedevices which are arranged at both sides of the suppressor device.

In another embodiment, the buried layer and the well are defined in asame region from top view.

The objectives, technical details, features, and effects of the presentinvention will be better understood with regard to the detaileddescription of the embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows atypical transient voltage suppressor (TVS) circuit 1.

FIGS. 1B-1D show several embodiments of the suppressor device of the TVScircuit according to the present invention.

FIG. 2 shows a preferable arrangement of the diode devices in the TVScircuit according to the present invention.

FIGS. 3A-3B show a cross-section view and a simulated impurityconcentration distribution of a diode device 100 in a prior art TVScircuit, respectively.

FIGS. 4A and 4B show a first embodiment of the present invention.

FIG. 5 shows a second embodiment of the present invention.

FIG. 6 shows a third embodiment of the present invention.

FIG. 7 shows a schematic top view of a diode device 200 of the firstembodiment.

FIG. 8 shows characteristic curves of TVS circuits 100 and 200 of theprior art and the present invention, respectively.

FIG. 9 shows temperature versus current characteristic curves of the TVScircuits 100 and 200 of the prior art and the present inventionrespectively, in an electrostatic discharge (ESD) test.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings as referred to throughout the description of the presentinvention are for illustration only, to show the interrelations betweenthe regions and the process steps, but not drawn according to actualscale.

Please refer to FIGS. 4A and 4B for a first embodiment according to thepresent invention, wherein FIG. 4A is a cross-section schematic diagramshowing a diode device 200 for a transient voltage suppressor (TVS)circuit according to the present invention. As shown in FIG. 4A, thediode device 200 is formed in a substrate 21 which has an upper surface21 a, wherein the substrate 21 is for example but not limited to aP-type substrate (or an N-type substrate in another embodiment). Next,for example but not limited to an N-type well 23 is formed beneath theupper surface 21 a in the substrate 21, and a buried layer 24 is formedbeneath the well 23 in the substrate 21. The buried layer 24 has a sameconductive type with the well 23 (N-type in this embodiment), and theimpurity concentration of the buried layer 24 is higher than that of thewell 23. The sequence order of the ion implantation process steps forthe buried layer 24 and the well 23 may be interchanged. Then, a fieldoxide region 22 and isolation regions 22 a are formed on the uppersurface 21 a of the substrate 21. The field oxide region 22 is locatedin the well 23 from top view (not show). The field oxide region 22 andthe isolation region 22 a for example are a local oxidation of silicon(LOCOS) structure or a shallow trench isolation (STI) structure, theformer being shown in the figure. Next, a P-type anode region 25 and anN-type cathode region 26 are formed beneath the upper surface 21 a attwo sides of the field oxide region 22 respectively, wherein the cathoderegion 26 is separated from the anode region 25 by the field oxideregion 22.

Referring to FIG. 4B shows a simulated impurity concentrationdistribution curve along a dash arrow line shown in FIG. 4A of the firstembodiment. In FIG. 4B, the vertical axis indicates the impurityconcentration, and the horizontal axis indicates a depth from the uppersurface 21 a. The impurity concentration distribution curve shown inFIG. 4B indicates the relationship between the depth and the impuritydistribution of the P-type anode region 25, the N-type well 23, theN-type buried layer 24, and the P-type substrate 21. Comparing theimpurity concentration distribution curves of the prior art and thepresent invention shown in FIGS. 3B and 4B, the buried layer 24 which isformed beneath the well 23 in this embodiment is an additional layer tothe prior art. This arrangement is advantageous in that: First, thediode device in the TVS circuit of the present invention can sustain arelatively higher transient forward current due to the additional buriedlayer with higher impurity concentration, and thus the application rangeof the TVS circuit is broadened. Second, in manufacturing process, noadditional mask is required, that is, the well 23 and the buried layer24 may be formed without any additional mask, requiring only oneadditional implantation process step which forms the buried layer 24. Assuch, the TVS circuit according to the present invention can bemanufactured by a low cost.

More specifically, when the protected circuit operates in a normaloperation condition, i.e., when the whole circuitry operates with arelatively lower voltage and current, the operation speed of theprotected circuit is primarily related to a relatively lower capacitanceformed by the P-type anode region 25 and the N-type well 23 in the diodedevice 200, which is comparable to the capacitance of the prior artdiode device 100. On the other hand, when a transient signal (such as anelectrostatic signal) with a high voltage and current is applied to thecircuitry, the transient signal can be released through the diode device200 with a higher capacitance which is formed by the P-type anode region25 and the N-type buried layer 24 because of the higher N-type impurityconcentration of the buried layer 24, such that the diode device 200 cansustain a higher forward current compared to the prior art diode device100. In summary, when the protected circuit is coupled to the TVScircuit of the present invention, the operation speed is faster or atleast comparable to the prior art in the normal operation condition, andthe circuitry can sustain a higher current once a transient signal (suchas an electrostatic signal) with a high voltage and current is appliedto the circuitry, because the TVS circuit of the present invention has ahigher transient capacitance. The higher transient capacitance of theTVS circuit according to the present invention can sustain and release ahigher current, such that the protected circuit can sustain a highertransient voltage and current, to enhance its ability against the ESD(Electro-Static discharge).

FIG. 5 is a schematic diagram showing a cross-section view of a diodedevice 300 in the TVS circuit of the present invention, which is asecond embodiment of the present invention different from the firstembodiment. As shown in the figure, the diode device 300 is formed in asubstrate 31, and includes a field oxide region 32, isolation region 32a, a P-type well 33, a P-type buried layer 34, a P-type anode region 35,and an N-type cathode region 36. This embodiment indicates that, thediode device according to the present invention may include the N-typewell and buried layer (such as the first embodiment), or the P-type welland buried layer (such as the second embodiment). Note that in bothembodiments the conductive type of the well and the buried layer is thesame, and the impurity concentration in the buried layer is higher thanthat in the well.

FIG. 6 is a schematic diagram showing a cross-section view of a diodedevice 400 in the TVS circuit of the present invention, which is a thirdembodiment of the present invention different from the first embodiment.As shown in the figure, the diode device 400 is formed in a substrate41, and includes an intrinsic semiconductor region 42, an N-type well43, an N-type buried layer 44, a P-type anode region 45, and an N-typecathode region 46. This embodiment indicates that, in the diode deviceaccording to the present invention, an intrinsic semiconductor regionmay be used to separate the anode region and the cathode region insteadof the field oxide region. The intrinsic semiconductor region is asemiconductor region without or with a low impurity concentration.

FIGS. 1B-1D and 2 show several embodiments of the suppressor device inthe TVS circuit according to the present invention. As shown in FIGS.1B-1D and 2, the suppressor device is for example but not limited to avaristor device V1 as shown in FIG. 1B, a Zener diode D2 as shown inFIG. 1C, two Zener diodes D2 connected in reverse series, or a gate-lessmetal oxide semiconductor (MOS) device Q1.

FIG. 2 also shows a preferable arrangement of the TVS circuit accordingto the present invention. As shown in FIG. 2, multiple diode devices Dpand Dn are arranged at both sides of the suppressor device (in thisembodiment, the MOS device Q1), wherein the diode device Dp includes forexample but not limited to N-type well and N-type buried layer, and thediode device Dn includes for example but not limited to P-type well andP-type buried layer.

FIG. 7 is a schematic diagram showing a top view of the diode device 200in the first embodiment of the present invention. As shown in the topview of FIG. 7, the buried layer 24 and the well 23 of the diode device200 are defined in a same region, i.e., they are overlapped; thus, theymay be defined by a same lithography process step. In this manner, theTVS circuit according to the present invention can better sustain atransient signal having a high voltage and current, but almost withoutincreasing the manufacturing cost.

FIG. 8 shows characteristic curves of the capacitance versus the voltagein the TVS circuits 100 and 200 of the prior art and the presentinvention, respectively. As shown in the figure, the two characteristiccurves are substantially overlapped, which indicates that, when theprotected circuit operates in the normal condition, the capacitances ofthe TVS circuits 100 and 200 are about the same. The reason has beenexplained in the above description. FIG. 8 indicates that the additionalburied layer of the present invention does not impact the capacitance ofthe circuitry in a normal operation, and thus the operation speed of theprotected device is not impacted.

FIG. 9 shows temperature versus current characteristic curves of the TVScircuits 100 and 200 of the prior art and the present inventionrespectively, in an ESD test. In a predetermined temperature range, themaximum transient currents of the transient signal which the TVScircuits 100 and 200 can sustain are indicated by the characteristiccurves shown in FIG. 9. According to the figure, the TVS circuit 200 ofthe present invention can sustain a higher forward current compared tothe prior art TVS circuit 100. In summary, referring to FIGS. 8 and 9,the TVS circuit according to the present invention can sustain a highertransient current without impacting the operation speed in the normaloperation condition; or, from another perspective, the present inventioncan enhance the operation speed of the protected circuit in the normaloperation condition with the same maximum transient current as the priorart.

The present invention has been described in considerable detail withreference to certain preferred embodiments thereof. It should beunderstood that the description is for illustrative purpose, not forlimiting the scope of the present invention. Those skilled in this artcan readily conceive variations and modifications within the spirit ofthe present invention. For example, other process steps or structureswhich do not affect the primary characteristic of the device, such as adeep well, etc., can be added. For another example, the order of theprocess steps for manufacturing the diode device may be interchanged;for example, the well and the buried layer can be formed before or afterthe field oxide region. For yet another example, it is described thatthe well and the buried layer may be defined by a same mask, but inanother embodiment, they may be formed by blanket implantation withoutany mask. In view of the foregoing, the spirit of the present inventionshould cover all such and other modifications and variations, whichshould be interpreted to fall within the scope of the following claimsand their equivalents.

1.-9. (canceled)
 10. A manufacturing method of a diode device for atransient voltage suppressor (TVS) circuit, wherein the TVS circuitincludes a suppressor device having a PN junction, and the diode devicehas a PN junction which is coupled to the PN junction of the suppressordevice in a reverse direction, the manufacturing method comprising:providing a first conductive type substrate, which has an upper surface;forming a well having the first conductive type or a second conductivetype in the substrate beneath the upper surface, and forming a buriedlayer in the substrate below the well, wherein the buried layer has asame conductive type with the well, and its impurity concentration ishigher than that of the well; forming a separation region in thesubstrate beneath the upper surface, wherein the separation region islocated in the well from top view; forming a first conductive type anoderegion beneath the upper surface at one side of the separation region;and forming a second conductive type cathode region beneath the uppersurface at the other side of the separation region, wherein the cathoderegion is separated from the anode region by the separation region. 11.The manufacturing method of claim 10, wherein the separation regionincludes a field oxide region or an intrinsic semiconductor region. 12.The manufacturing method of claim 10, wherein the buried layer and thewell are defined in a same region from top view.